4130 is simply a better material for an engine mount. Lynn's comments were pretty much on point, 4130 is stronger, harder and much tougher. Stainless usually only is truly rust resistant if passivated or electropolished after welding. The welding process brings some of the iron to the surface and the area around the weld will rust in the area of discoloration. Stainless is VERY subject to hydrogen embrittlement too. This can cause cracking on welded structures used in vibrating assemblys. 4130 isn't as subject to H2 embrittlement. So there are lots of reasons to use 4130. If the structure is suitably overbuilt this might not be a problem, but you better be sure of that. A engine mount failure is a VERY BAD thing on a autogyro.
Ernest,
"""> Thomas, I don't see the benefit of stainless being the protection of the
> inside of the tube......""""
I don't like stainless at all , unless there is no workable alternative...
Rusty wants the bling on the thing!!
Thomas
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